Field of the Invention
The present invention relates to a test bench for characterizing a flow of a two-phase fluid, in particular a flow of fuel for feeding to a turbine engine, such as an airplane turboprop or turbojet.
Description of the Related Art
Such a turbine engine is conventionally provided with a fuel pump having a low pressure stage, referred to as the low pressure pump, and a high pressure stage, referred to as the high pressure pump. The low pressure pump is for generating a pressure rise, and it is generally formed by a centrifugal pump having a bladed impeller. Its pressure raising characteristics depend strongly on the speed of rotation of the pump. The high pressure pump is for generating a flow rate. These two pumps are usually incorporated in a common housing and they are driven at the same speed by a shaft.
Physical phenomena modify significantly the characteristics with which the turbine engine is fed in operation, these phenomena depending in particular on the shape of the fuel feed pipe, on altitude, and on the type of fuel used. In particular, in operation, air dissolved in the fuel (kerosene) tends to gas out and the kerosene can vaporize. The fluid flowing in the pipe and through the fuel pump is thus a two-phase fluid containing bubbles or pockets of gas that can lead to malfunctions of the turbine engine (fluctuations in thrust, loss of control, engine stopping, etc.).
For safety reasons, it is necessary to be able to guarantee that turbine engines can tolerate this type of phenomenon, regardless of operating conditions. Nevertheless, these phenomena are poorly known at present and it is relatively difficult to model them or to reproduce them during testing. It therefore appears to be necessary to be able to study and to characterize such phenomena. In particular, such characterization involves having knowledge of the ratio representing the proportion of the vapor phase relative to the liquid phase of the fuel.
At present, the only standard dealing with the quantity of gas and the gas factor in an airplane fuel feed system is the ARP 492 standard. That standard is relatively old and does not enable the above-mentioned phenomena to be studied reliably.
For safety reasons, present-day pumps are overdimensioned so as to guarantee proper operation of the turbine engine under all operating conditions. Nevertheless, such overdimensioning is unfavorable in terms of weight and size, in particular.